The present invention relates to image sensing apparatuses having CCD-type image sensing elements.
The commercial spread of digital still cameras (DSC) with CCD sensing elements has been tremendous. Such image sensing elements are configured of a plurality of photoelectric conversion portions, a plurality of vertical transfer portions, a horizontal transfer portion, and a charge detection amplifier. The photoelectric conversion portions are arranged as pixels in the horizontal direction and the vertical direction, and are for the photoelectric conversion of the subject image. The vertical transfer portions are for the vertical transfer of the charges in the pixels. The horizontal transfer portion is for the horizontal transfer of the charges that have been transferred by the vertical transfer portions. The charge detection amplifier converts the charge signal obtained from the horizontal transfer portion into a voltage signal, and outputs it as the image sensing signal. For the vertical transfer portions, there are interlace-type vertical transfer portions provided with two charge holding portions for each photoelectric conversion portion, and progressive-type vertical transfer portions with three or four charge holding portions for each photoelectric conversion portion.
In DSCs of recent years, there is a demand for providing moving pictures with higher definition than conventional TV pictures at low cost, in addition to high-definition still images. Furthermore, there is a need for the display of high-definition moving pictures not only on TV sets but also on display devices of personal computers.
In DSCs using a CCD image sensing element with 1,300,000 pixels for example, the effective pixel number is 1280 horizontal pixels and 960 vertical pixels, and when so-called interlaced readout is performed, moving pictures with a picture quality that is close to Hi-Vision can be attained.
However, in this case, the driving frequency of the horizontal transfer portion is as high as about 50 MHz. Driving the horizontal transfer portion at such high speeds increases the power consumption, leads to a high degree of technical difficulty with small margins for performance guarantee, and necessitates adjustments or the like, so that the costs become extremely high.
It is an object of the present invention to provide an image sensing apparatus with which the driving frequency of the horizontal transfer portion can be reduced, while obtaining high-definition moving pictures.
To attain this object, in the present invention, the charges of four pixels of the image sensing element that are adjacent in the horizontal direction and the vertical direction are mixed and output.
More specifically, a first image sensing apparatus in accordance with the present invention includes an image sensing element having a plurality of photoelectric conversion portions for photoelectric conversion of a subject image, the photoelectric conversion portions being arranged as pixels in horizontal direction and vertical direction, and a mixing means for mixing and outputting charges of four pixels of the image sensing element that are adjacent in the horizontal direction and the vertical direction, wherein combinations of the pixel mixings in the horizontal direction are changed at each line, so that the signals after the four pixels have been mixed are in an offset sampling relation for each line. With this configuration, the horizontal driving frequency during the image sensing of moving pictures can be set to xc2xd of the case that pixel mixing in the horizontal direction is not performed. Moreover, by employing offset sampling, it is possible to prevent deterioration of the horizontal resolution. Furthermore, if the combination of pixel mixings in the vertical direction is changed for each field, then it is possible to adapt to Hi-Vision interlaced scans.
A second image sensing apparatus in accordance with the present invention includes an image sensing element having a plurality of photoelectric conversion portions for photoelectric conversion of a subject image, the photoelectric conversion portions being arranged as pixels in horizontal direction and vertical direction, a mixing means for mixing and outputting charges of four pixels of the image sensing element that are adjacent in the horizontal direction and the vertical direction, and a control means for selecting and controlling an operation mode in which signals of all pixels are output independently without performing the four-pixel mixing, and an operation mode in which signals after the four pixels have been mixed are output, wherein the image sensing element is provided with a color filter arrangement with which in both operation modes at least three independent color signals are obtained. Thus, in addition to still pictures that are equivalent to the prior art, it is possible to obtain high-definition moving pictures.
A third image sensing apparatus in accordance with the present invention includes an image sensing element having a plurality of photoelectric conversion portions for photoelectric conversion of a subject image, the photoelectric conversion portions being arranged as pixels in horizontal direction and vertical direction, a mixing means for mixing and outputting charges of four pixels of the image sensing element that are adjacent in the horizontal direction and the vertical direction, a control means for changing for each frame the combination of pixel mixings in the horizontal direction in the four-pixel mixing, and a pixel synthesis portion for synthesizing an image of two frames with different combinations of pixel mixings in the horizontal direction. Thus, the image quality of moving pictures can be improved even more than with the second image sensing apparatus.